Monday, August 5,1878 – Sam and Joe left by Baden-Baden rail to Achern, for a week-long tramp. He describes this first day in a letter to Livy:

Sunday, August 4, 1878: Sam and Joe took another one-day excursion from Baden Baden to Ebersteinburg to Nuehaus to Gernsbach, where they drank beer. The pair returned to Baden Baden in the evening. (DBD)

Friday, August 2, 1878: Sam and Joe took a short excursion (6 miles) to the popular Altes Schloss (Favorita Schloss), a conspicuous ruin on the summit of a hill outside town. Sam’s notebook holds an entry paraphrasing a guide book, that:
“...no tourist should fail to climb the mountain & enjoy the view. Hired boy to climb the Mt & examine (or enjoy?) the view. He felt well repaid for all his trouble.”
Later in the day they walked back through the woods to Baden Baden.
(DbyD)

See A Carriage Ride Through the Back Forest

July 24, 1878: The Clemens party started out on a three-day carriage trip through the Black Forest. They stayed at inns along the route.

The party more than likely took what Bædeker describes as the direct route to Forbach:

Railways:

The Main-Neckar Railway (German: Main-Neckar–Eisenbahn, MNE) is a main line railway west of the Odenwald in the Upper Rhine Plain of Germany that connects Frankfurt am Main to Heidelberg via Darmstadt, Bensheim and Weinheim. It was opened in 1846 and is one of the oldest railways in Germany.

The Main-Neckar Railway was built and operated as a joint state railway company, known as a condominium railway (Kondominalbahn), by the Free City of Frankfurt, The Grand Duchy of Hesse-Darmstadt and the Grand Duchy of Baden.

After leaving Hamburg, the Clemens party traveled by rail to Heidelberg, stopping briefly in Hanover, Wilhelmshohe, Cassel, and Frankfort on the Main. The prettiest effect is a cloud-ceiling in fresco in our parlor at Frankfort. German cleanliness reaches an altitude to which we may not aspire. These peasants are as cleanly in their houses as the Yankee of romance & more cleanly than the reality.

November 15, 1878 - February 27th, 1879: Arriving from Rome, Italy: November 17 Sunday – Sam wrote from Munich, Germany to Howells, giving him the itinerary of the trip from Rome. (see From Rome to Munich)